Hydraulic double telescopic prop

ABSTRACT

The double telescopic prop comprises an outer cylindrical casing tube  1 , an inner tube  2  which is displaceable therein and a piston rod  3  which can be extended therefrom. The hydraulic fluid for extending the two prop stages is conveyed through a connection  14  to the piston  5  of the inner tube  2  and is conveyed via a bottom valve to the piston  7  of the piston rod  3 . The prop is retracted if hydraulic fluid flows via the connection  17  into the outer annulus  11  between the cylindrical casing tube  1  and the inner tube  2 . A size ratio of 8.8:1 at most, which is favourable for the retraction of the prop, exists between the area of the inner tube  2  and the ring area of the annulus  11.

DESCRIPTION

A hydraulic double telescopic prop comprising an outer cylindricalcasing tube, an inner tube which is displaceable therein and a pistonrod which can be extended therefrom, having an outer annulus between thecylindrical casing tube and the inner tube and having an inner annulusbetween the inner tube and the piston rod, wherein the pressure mediumcan be fed under a piston of the inner tube and via a bottom valve underthe piston rod in order to extend the two pressure stages, and can befed into the outer and inner annuli for retraction.

Two-stage double telescopic props of the aforementioned type are usedunderground in mining in combination with hydraulic self-advancingsupports. In order to support the exposed overlying stratum in alongwall face with a high shaft lining supporting force during themining of coal, props of large volume are required, with acorrespondingly high requirement for pressure medium. The constructionof the props for static loading purposes is fashioned in accordance withthe requirements imposed, and the prop tubes and piston rod are designedwith suitable cross-sections and wall thicknesses. In turn, thedimensions selected have an effect on the sizing of the nominaldiameters of the control valves and of the supply lines containinghydraulic fluid. These relationships ultimately determine the propertiesof a prop, which apart from the supporting force of the prop alsoinclude its drawing-in properties, which are important for shifting thewall lining during the reverse operation. For drawing-in, i.e. forretracting the placed prop, the pressure space in the outer cylindricalcasing tube is connected to the return line to the tank, so thathydraulic fluid can drain off and the prop can sink. Hydraulic fluid isat the same time introduced into the outer annulus between thecylindrical casing tube and the inner tube. This hydraulic fluid acts onthe ring area on the piston of the inner tube and pushes it in. Theforce which is generated on the small pressurised ring area fordrawing-in the prop is slight, however. In contrast, a resistance toflow occurs in the control valve when the hydraulic fluid is expelledfrom the prop space of large volume, and moreover this resistance toflow is increased by a banking-up pressure in the return line ifhydraulic fluid simultaneously flows into the return line from otherconsumers of hydraulic fluid.

The consequence is a slow sinking-in of the prop and a delay in theprogress shaft lining shifting operation. A structural enlargement ofthe ring area would inevitably increase the external dimensions of theprop or would impair the static loading properties of the prop if itwere carried out at the expense of the internal dimensions of the prop.Both of these effects are undesirable.

The present invention stems from background art from internaloperations. According to this, hydraulic double telescopic props areconstructed in such a way that the outer annulus between the cylindricalcasing tube and the inner tube, which annulus is acted upon by hydraulicfluid during the drawing-in operation, has a relatively narrow aperturewidth, so that a size ratio of at least 10:1, which is unfavourable asregards the sinking-in behaviour of the prop, is achieved between thepiston area of the inner tube and the ring area. On the other hand, thesmaller size ratio of the inner ring area to the piston rod area remainsunutilised, because the piston rod is generally not retracted during ashaft lining shifting operation.

The underlying object of the present invention is to fashion the staticloading construction of a telescopic prop of the type cited at theoutset, whilst retaining its external dimensions, in such a way that theforce available for drawing-in is increased whilst the supporting forceremains constant.

The double telescopic prop exhibits an advantageous relation of itsdimensions to the form of the inner prop construction, in order toincrease the ring area over the piston of the inner tube whilst thepredetermined external dimensions and supporting forces remainunchanged, and in order to intensify the force for drawing-in the prop.

Since neither the requisite wall thicknesses of the prop tubes nor thepiston rod diameter are changed, the static loading construction of theprop remains unchanged. The greater force is utilised for speeding upthe drawing-in process, because at the higher liquid pressure a largeramount of liquid can also flow out of the pressure space of the propinto the return line. This saving in time when drawing in the propspeeds up the shaft lining shifting operation. There is thus anavoidance of delays in shaft lining such as those which occur in modernhigh output operations when a mining machine with a high cutting speedrushes ahead of the shifting of the shaft lining, because the shiftingoperation requires more time than does the mining of coal, so that theshaft lining remains behind.

The invention is explained in more detail below with reference to anexample of an embodiment which is illustrated in the drawing. Thedrawing shows a hydraulic double telescopic prop in its retracted ordrawn-in state, the right half of which is illustrated in longitudinalsection.

The prop is of two-stage construction, and comprises an outercylindrical casing tube 1, an inner cylindrical tube, the inner tube 2and a piston rod 3, wherein the inner tube 2 is axially displaceablyguided in the cylindrical casing tube 1 and the piston rod 3 is axiallydisplaceably guided in the inner tube 2. The bearing of the prop on thefootwall side is formed by a hemispherical prop base 4, which terminatesthe cylindrical casing tube 1 at the bottom. The inner tube 2 isterminated on the footwall side by an inner tube piston 5 of largerdiameter with a stepped reduction, in which piston a bottom valve 6 isinserted. The footwall end of the piston rod 3 is likewise of largerdiameter than its shank, with a stepped reduction, and is constructed asa piston 7, a recess 8 in which encompasses the protruding part of thebottom valve 6. A prop head 9 is situated at the top end of the pistonrod 3.

At its footwall end, the inner tube 2 is guided with its inner tubepiston 5 on the inner wall of the cylindrical casino tube 1, and at itshead end it is guided in a flange-like threaded ring 10 on the outerwall, which threaded ring is screwed into the cylindrical casing tube 1from above. An outer annulus 11 with an aperture width d₁−d₂ is thusformed between the inner wall of the cylindrical casing tube 1 ofdiameter d₁ and the outer wall of the inner tube 2 of diameter d₂.

In the same manner, the piston rod 3, which slides with its piston 7 onthe inner wall of the inner tube 2—diameter d₃—is guided by a threadedring 12 which is inserted in the top end of the inner tube 2. Thediameter of the shank of the piston rod 3 is denoted by d₄. The innerannulus 13 of aperture width d₃−d₄ is formed between the inner tube 2and the piston rod 3.

The hydraulic fluid is conveyed under the inner tube piston 5, from aconnection 14 and via a bore 15, into the lower stage of the prop,whereupon the pressure space, which is not marked, in the interior ofthe cylindrical casing tube 1 is filled, so that the inner tube 2 movesout until the inner tube piston 5 comes into contact with the threadedring 10. The hydraulic fluid continues to flow via the bottom valve 6into the pressure space, which is likewise not marked, in the inner tube2 of the upper stage, so that the piston rod 3 is also pushed out untilthe piston 7 comes into contact with the threaded ring 12. The bottomvalve 6 is a non-return valve which separates the pressure spaces of thelower stage and of the upper stage from each other. Consequently, ahigher pressure can build up in the upper stage than in the lower stage,due to the different area ratios.

Whilst the inner tube is moving out during the placement operation,hydraulic fluid is displaced by the inner tube piston 5 from annulus 11into the return line, via the bore 16 and the connection 17. Annulus 11is connected to annulus 13 by a channel 18 which extends in the wall ofthe inner tube 2, so that the hydraulic fluid can emerge from annulus 13when the piston rod 3 is extended.

In order to retract the pressure stages during a drawing-in operation,hydraulic fluid is introduced into the outer annulus 11 in the oppositedirection through the connection 17. The hydraulic fluid acts on theinner tube piston 5 over the ring area of aperture width d₁−d₂, so thatthe inner tube 2, together with the piston rod 3, is pushed into thepressure space of the cylindrical casing tube 1, from which thehydraulic fluid emerges into the return line via the connection 14. Theupper stage is not depressurised at first, because the hydraulic fluidcannot flow out of the pressure space in the inner tube 2 through theclosed bottom valve 6.

The bottom valve 6 is not pushed open until the inner tube piston 5 ofthe inner tube 2 comes into contact with the prop base 4. Hydraulicfluid then flows into the inner annulus 13 via connection 14 and channel18, and acts on the piston 7 over the ring area of aperture width d₃−d₄,so that the piston rod 3 is pushed into the pressure space of the upperstage.

According to the invention, the aperture width d₁−d₂ of the outerannulus 11 is greater than or equal to the aperture width d₃−d₄ of theinner annulus 13. The wall thicknesses of the outer cylindrical casingtube 1 and of the inner tube 2 are likewise approximately the same.

The piston area $\left( \frac{d_{1}}{2} \right)^{2} \cdot \pi$

of the inner tube 2 and the ring area${\left( \frac{d_{1}}{2} \right)^{2} \cdot \pi} - {\left( \frac{d_{2}}{2} \right)^{2} \cdot \pi}$

of the outer annulus 11 are in a size ratio of less than or equal to 8.5to each other.

The piston area $\left( \frac{d_{3}}{2} \right)^{2} \cdot \pi$

of the piston area rod 3 and the ring area${\left( \frac{d_{3}}{2} \right)^{2} \cdot \pi} - {\left( \frac{d_{4}}{2} \right)^{2} \cdot \pi}$

of the outer annulus 11 are in a size ratio of greater than or equal to5.51 to each other.

What is claimed is:
 1. A hydraulic double telescopic prop comprising anouter cylindrical casing tube, an inner tube which is displaceabletherein and a piston rod which is selectively extended therefrom, havingan outer annulus between the cylindrical casing tube and the inner tubeand having an inner annulus between the inner tube and the piston rod,wherein the pressure medium is selectively fed under a piston of theinner tube and via a bottom valve under the piston rod in order toextend the two pressure stages, and is selectively fed into the outerand inner annuli for retraction, characterised in that an aperture width(d₁−d₂) of the outer annulus (11) is designed so that it is greater thanor equal to an aperture width (d₃−d₄) of the inner annulus (13), and asize ratio of a piston area on the inner tube (2) to a ring area of theouter annulus (13) is less than or equal to 8.5:1, whilst a size ratioof a piston area on the piston rod (3) to a ring area of the innerannulus (13) is greater than or equal to 5.5:1.
 2. A hydraulic doubletelescopic prop according to claim 1, characterised in that the outercylindrical casing tube (1) and the inner tube (2) have approximatelythe same wall thicknesses.